Arrested fly ash samples from most currently operating municipal solid waste (MSW) incinerators on the U.K. mainland have been analysed for polynuclear aromatic hydrocarbons (PAHs). The ashes have a mean PAH content of about 227 µg kg -1. This is generally lower than concentrations observed in U.K. surface soils. Benzo-[ghi]perylene was the most abundant individual compound, and the most frequently detected. The PAH content of ashes does not appear to be related to incinerator type, but rather it is likely that poor gas phase combustion favours higher PAH levels. The significance of PAHs in ash residues and their possible fate following disposal to landfill are discussed.